In recent days, with the progress of high performance and high functionality in semiconductor devices and electronic devices, the amount of heat generation from them has been increasing. Therefore, a cooling device with high heat transportation capability has been required. The cooling device using a phase-change cooling system in which the heat transportation and heat radiation are performed by a phase-change cycle of vaporization and condensation of a refrigerant makes it possible to improve the heat transportation capability compared to a heat sink and the like. The cooling device is therefore expected as a cooling device for the semiconductor device and the electronic device with a large amount of heat generation.
An example of the cooling device using the phase-change cooling system (hereinafter, also referred to as “a phase-change cooling device”) is described in Patent Literature 1. The related phase-change cooling device described in Patent Literature 1 is used in order to cool a semiconductor device as a heat generation source such as a CPU (central processing unit) mounted on a circuit board. The related phase-change cooling device includes an evaporating unit attached on the surface of a semiconductor device and a condenser having a radiator, and between those are attached a pair of conduits composed of a vapor tube and a liquid return tube. The related phase-change cooling device is made to keep its inside to be a reduced (low) pressure condition of approximately one-tenth of the atmospheric pressure, and configures a thermosiphon which can circulate a refrigerant without external motive force such as an electro-motive pump due to the phase change of the water of a liquid refrigerant.
In the related phase-change cooling device, the heat generated in the semiconductor device of a heat generation source is transferred to the evaporating unit. As a result, in the evaporating unit, the water of the liquid refrigerant is boiled and evaporated under the reduced pressure due to the transferred heat, and the generated vapor is guided from the evaporating unit into the condenser through the vapor tube. In the condenser, the refrigerant vapor is cooled by an air blown by a cooling fan to become liquid (water), and then it turns back into the evaporating unit again through the liquid return tube due to the gravity.
On the other hand, with electronic devices being miniaturized and made thinner, a connecting structure is required which connects the cooling device to the semiconductor device corresponding to miniaturizing and making thinner. Patent Literature 2 describes an example of the connecting structure of the cooling device to be mounted on the electronic device which can be made thinner.
The related electronic apparatus described in Patent Literature 2 includes in housing, a circuit board, first and second heating elements, first and second sub heat pipes, a main heat pipe, first and second pressing members, a heat sink, and a cooling fan. The first pressing member presses a first portion of the first sub heat pipe to the first heating element and strengthens the thermal connection between the first sub heat pipe and the first heating element. At this time, the first sub heat pipe is pressed to the first heating element by the first pressing member and can be bent following the inclination or the shape of a die of the first heating element.
Therefore, the first sub heat pipe is less likely to come into partial contact with the die of the first heating element.
In the related electronic apparatus, the main heat pipe with a relatively large length, a relatively large thickness, and high heat transport performance is arranged at a position offset from the heating element, and the sub heat pipe is provided between the main heat pipe and the heating element. That is to say, in the related electronic apparatus, the plate-shaped sub heat pipe with a small thickness is overlapped on the circuit board and the heating element, and the main heat pipe with a relatively large thickness is arranged in a region where it does not overlap with the heating element. It is said that the configuration makes it possible to reduce the overall thickness of a heat radiating structure and thus reduce the thickness of the electronic apparatus.